What could cause elevated immunoglobulin M (IgM)? IgM result is 468 mg/dl, all other bloodwork normal. Also shortness of breath, shoulder, rib pain

Infection, myeloma. IgM is the 1st antibody released by the immune system in the course of fighting an infection. Depending on the amount of other antibodies (even if normal), it could also represent a tumor or malignancy of the immune system, like lymphoma or myeloma. We can't diagnose that here. Use HealthTap Prime to upload the entire report (all tests) or talk to the doctor who ordered the bloodwork. Good luck.